In lithographic printing, ink receptive regions, known as image areas, are generated on a hydrophilic surface. When the surface is moistened with water and ink is applied, the hydrophilic regions retain the water and repel the ink, the ink receptive regions accept the ink and repel the water. The ink is then transferred to the surface of suitable materials upon which the image is to be reproduced. In some instances, the ink can be first transferred to an intermediate blanket that in turn is used to transfer the ink to the surface of the materials upon which the image is to be reproduced.
Imageable elements useful to prepare lithographic (or offset) printing plates typically comprise one or more imageable layers applied over a hydrophilic surface of a substrate (or intermediate layers). The imageable layer(s) can comprise one or more radiation-sensitive components dispersed within a suitable binder. Following imaging, either the exposed regions or the non-exposed regions of the imageable layer(s) are removed by a suitable developer, revealing the underlying hydrophilic surface of the substrate. If the exposed regions are removed, the element is considered as positive-working. Conversely, if the non-exposed regions are removed, the element is considered as negative-working. In each instance, the regions of the imageable layer(s) that remain are ink-receptive, and the regions of the hydrophilic surface revealed by the developing process accept water or aqueous solutions (typically a fountain solution), and repel ink.
Similarly, positive-working compositions can be used to form resist patterns in printed circuit board (PCB) production, thick-and-thin film circuits, resistors, capacitors, and inductors, multichip devices, integrated circuits, and active semiconductive devices.
“Laser direct imaging” methods (LDI) have been known that directly form an offset printing plate or printing circuit board using digital data from a computer, and provide numerous advantages over the previous processes using masking photographic films. There has been considerable development in this field from more efficient lasers, improved imageable compositions and components thereof.
Thermally sensitive imageable elements can be classified as those that undergo chemical transformation(s) in response to, exposure to, or adsorption of, suitable amounts of thermal energy. The nature of thermally induced chemical transformation may be to ablate the imageable composition in the element, or to change its solubility in a particular developer, or to change the tackiness or hydrophilicity or hydrophobicity of the surface layer of the thermally sensitive layer. As such, thermal imaging can be used to expose predetermined regions of an imageable layer that can serve as a lithographic printing surface or resist pattern in PCB production.
Positive-working imageable compositions containing novolak or other phenolic polymeric binders and diazoquinone imaging components have been prevalent in the lithographic printing plate and photoresist industries for many years. Imageable compositions based on various phenolic resins and infrared radiation absorbing compounds are also well known.
WO 2004/081662 (Memetea et al.) describes the use of various developability-enhancing compounds of acidic nature with phenolic polymers or poly(vinyl acetals) to enhance the sensitivity of positive-working compositions and elements so that required imaging energy is reduced. Some of the particularly useful poly(vinyl acetals) for such compositions and elements are described in U.S. Pat. No. 6,255,033 (Levanon et al.) and U.S. Pat. No. 6,541,181 (Levanon et al.).
Thermally imageable elements containing certain developability-enhancing materials and poly(vinyl acetal)s are described in copending and commonly assigned U.S. Ser. No. 11/677,599 (filed Feb. 22, 2007 by Levanon, Postel, Rubin, and Kurtser), Ser. No. 11/769,766 (filed Jun. 28, 2007 by Levanon, Lurie, and Kampel), and Ser. No. 11/959,492 (filed Dec. 18, 2007 by Nakash and Levanon).
Imageable elements containing phenolic resins are described in U.S. Pat. No. 6,410,203 (Nakamura). After imaging, the elements are developed with any of a variety of developers including silicate-containing, carbonate, phosphate, and borate developers.
Copending and commonly assigned U.S. Ser. No. 12/025,089 (filed Feb. 4, 2008 by Levanon, Nakash, and Kurtser) and Ser. No. 12/125,084 (filed May 22, 2008 by Levanon and Nakash) describes the use of carbonate developers for processing positive-working imageable elements containing certain poly(vinyl acetal)s.
Problem to be Solved
Positive-working imageable elements are generally imaged and developed using various highly alkaline developers that contain silicates or metasilicates. While such developers are effective to remove imaged portions of the imageable layer, they can react undesirably with aluminum substrates and generate toxic waste solutions that create problems for disposal. Moreover, the silicates may accumulate in pipes and other parts of the processing apparatus.
In addition, after use of various developers, the printing plates are usually “gummed” with a conventional gum solution to provide a protective layer over the imaged surface. Thus, imaging, developing, water rinsing and gumming require multiple steps and stations in a processor.
There is a need to find a more environmentally acceptable and less costly way to develop imaged positive-working imageable elements, especially those having a single imageable layer containing poly(vinyl acetal) binder resins. There is also a need to simplify the process of providing a printable image in lithographic printing plates.